The present invention relates to a process for the production of homogeneous bar-shaped or granular-shaped thermoplastic compositions containing polymers and bitumen.
It is known that the property spectrum of bitumen can be improved by the addition of polymers, either thermoplastics, e.g. polyethylene, atactic polypropylene, polybutene, etc., or cross-linkable elastomers, e.g. natural rubber (NR), styrene-butadiene rubbers (SBR), polychloroprene rubbers (CR), acrylonitrile-butadiene rubbers (NBR), polybutadiene rubbers (BR), polyisoprene rubbers (IR), butyl rubbers (IIR), ethylene-.alpha.-olefin rubbers (EPM and EPDM), and ethylene-vinyl acetate or -acrylic acid or -acrylic acid ester copolymers; see, for example, U.S. Pat. No. 3,336,252; J. Appl. Chem. 7: 481-90 (1975); "Bitumen, Teere, Asphalte, Peche" [Bitumen, Tars, Asphalts, Pitches] 1966, issue 9; and Rubber Trend, March 1968.
Ethylene-.alpha.-olefin copolymers and the ethylene-.alpha.-olefin-diene terpolymers are particularly suitable for this purpose due to their excellent stability against longterm elevated temperatures during transport and storage, as well as against open-air weathering mainly caused by ultraviolet radiation or the action of ozone.
According to the disclosure in DAS [German Published Application] No. 1,939,926, corresponding to copending, commonly assigned U.S. Pat. No. 3,963,659, the contents of which are incorporated by reference herein, thermoplastic compositions are advantageously produced from bitumen and 0.5-25 parts by weight of an ethylene-.alpha.-olefin elastomer by preliminarily kneading the ethylene-.alpha.-olefin elastomer and adding the bitumen either in small incremental portions or gradually in a continuous fashion. Although homogeneous compositions are obtained in this way, the process is time-consuming and thus uneconomical.
Therefore, there still exists a need for a process wherein thermoplastic compositions of bitumen and saturated and unsaturated polyolefin elastomers are obtained in the particularly valuable forms of a bar or granules. These shapes provide marked advantages for both transportation and storage as well as for further processing operations, especially for direct incorporation into liquid bitumen. The present invention fills such needs.